1. Field of the Invention
The present invention relates to a device and a process for detecting defects in an arrangement (disposition) of reinforcing members. The reinforcing members may include magnetizable material, e.g., steel, in casing plies in the sidewall region of an unvulcanized tire blank or a vulcanized pneumatic vehicle tire.
2. Discussion of Background Information
Pneumatic vehicle tires are generally made with one or a plurality of casing plies having parallel reinforcing members imbedded inside. The casing plies usually extend from one bead core, over a sidewall, a crown region, another sidewall, and to a second bead core. While the crown region is usually additionally reinforced by belt plies, the sidewall gets its strength and resistance, i.e., relative to foreign bodies from outside and relative to internal pressure, mainly from reinforcing members within the casing. Accordingly, irregularities in the arrangement or positioning (spacing) of the reinforcing members of the casing can be particularly disadvantageous, especially in a vicinity of the sidewall. That is, irregularities, e.g., in the form of enlarged spaces between reinforcing members, lead to full-blown weak points of the sidewall. In the operating state of a vehicle, internal pressure of the tire can lead to excess strain of the rubber material and bulging and, in the long term, to the tearing of the rubber material. Because foreign bodies can penetrate this region with particular ease, tire blowouts may consequently result. Further, even smaller damages to the rubber material of the tire can easily lead to the tearing of the rubber material in the region of the weak point.
Since defects of the type described above, i.e., in the arrangement (spacing) of the reinforcing members, can still occur in a wide variety of ways during the construction of the tire and with the production of the torus form, it is important to utilize quality controls of the toroid pneumatic vehicle tire so as to achieve early detection of arrangement deviations of the reinforcing members in the sidewall region. These detected deviations exceed maximal permissible values based on experimental values. With retreads or used tires, it is also important to be able to detect these substantially impermissible irregularities early, e.g. after more intense contact of the sidewall with curb edges or other hard objects.
In the prior art, it is conventional for pneumatic vehicle tires having casings with reinforcing members of steel to be X-rayed after vulcanization. The tire is X-rayed all around the tire circumference. This permits the circumferential arrangement or position of impermissible arrangement deviations and the member sizes to be precisely determined by measuring the spacings. X-ray apparatuses of the type utilized in this environment generally require a large cost expenditure for installation and maintenance. Further, wear and tear on costly, sensitive X-ray tubes is considerably high. In order to protect the environment and the health of operating personnel, further high cost expenditures are necessary for additional devices, e.g., X-radiation shielding. Still further, when testing tires in series production, continuous optical evaluation of X-ray images, which exhibit a large number of parallel, closely adjacent, dark reinforcing members in the brightly lit surroundings, is fatiguing for operating personnel. Additional cost expenditures are necessary to protect against X-radiation and damage to the display unit due to fatigue when it is frequently actuated. The X-ray apparatus also requires a large number of additional subassemblies, e.g., for cooling, that are cost-intensive electronic equipment for control and evaluation of the overall X-ray apparatus. Further, the entire measuring station, with all of the corresponding protective measures and subassemblies and the large number of components, takes up a considerable amount of space.
Since a minimum measurement time is required for each tire measurement, an increase in the tire production beyond a particular measure signifies a requirement for installing additional cost-intensive X-ray apparatuses. These additional x-ray apparatuses, suffer from the disadvantages noted above, e.g. costly maintenance, protection, assembly, operation, and storage space. Due to the high cost, the x-ray apparatuses are generally only used at the end stage of tire production, in which all of the manufacture conditional arrangement or position deviations can be detected. Since positioning defects of the reinforcing members can also occur within the vulcanization apparatus and during vulcanization, X-ray apparatuses of the type discussed above are generally only used on the finished, vulcanized vehicle tire. However, tires having impermissible arrangement or position deviations, cannot be repaired when such defects are detected in this late, vulcanized state. Further, as scrap, these vulcanized finished tires can hardly be reused.
Due to the high expenditure necessary for maintaining and utilizing X-ray apparatuses, automobile shops and other maintenance personnel are generally unable to perform the above described checks during the service life of the tire. Even when the apparatuses are available, the checks are generally performed on a limited basis and at a significant cost.
German Patent document No. DE 42 23 248 A1 has disclosed the detection of defects in wide steel cord strips through the use of a magnetic field leakage process. For example, in the production of flat casing belts, the steel cord strips are drawn across a metal plate so that an angle of greater than 0.degree. is produced between the direction of movement and the alignment of the steel cords. Detectors of the type, e.g., SND 6 by Roland Electronik GmbH, D-7538 Keltern 2, which had previously been used for monitoring welding seams, are located beneath the metal plate. In this process, the detectors produce a heterogeneous magnetic field. The steel cord strips are moved through, and in a direction of, the magnetic field, to influence the heterogeneous magnetic field as a function of the spacing of the steel cords relative to each another. The detectors determine a magnetic field intensity resulting from induction arising at the defects and immediately indicate the magnetic field intensity change. The cord strip is stopped and the defective place is immediately removed so that the casing material, which is produced in belt form, can be used in a perfect state for further production of the tire. In this manner, defects in the casing material that exist in the production of the casing belts can be detected and removed.
However, arrangement or positioning defects between the reinforcing members of the casing, which are produced from the different plies and layers, in the transport of the plies to construction, in the raising the plies and layers for producing the torus shape, in the bonding of the casing packet with the tread and belt, in the raising and lowering of assembly drums, and/or in other actions after the manufacture of the flat, smooth, belt-shaped, half-finished casing product cannot be detected with the process and device of DE 42 23 248 A1. In order to detect defects of this kind, in a practical conversion, the aforementioned X-ray process, with all of its associated disadvantages, must be relied upon.